APTT MEASUREMENT USING PLATELET SUBSTITUTE MIXTURE

Test the control plasma and patient’s plasma in duplicate.

1. Pipette 0.2 ml of well-mixed kaolin/platelet substitute in a small glass tube.

2. Add 0.1 ml of plasma, mix, and incubate at 37° C for exactly 2 minutes (tilting the tube at intervals).

3. Add 0.1 ml 0.025 mol/l calcium chloride, mix and start the stop-watch. Hold the tube in the water bath and tilt the mixture back and forth, looking for clot formation. When a clot forms, stop the stop-watch and record the time.

4. Report the patient’s APTT (average of the duplicate tests) providing the APTT of the normal control plasma is satisfactory.

Reference APTT range

36–50 seconds

What causes prolonged APTT?

• DIC (involving several clotting factors)
• Deficiency of clotting factors: prothrombin, V, VIII, IX, X, XI or XII due to vitamin K deficiency, liver disease, heparin or warfarin anticoagulation, or less commonly an inherited coagulation disorder.

See also:

The Principle of APTT test